In general, a ferrous material is employed for a part for a compressor or a part for an oil pump. In the case of the ferrous material, however, its weight comes into question. Particularly when the ferrous material is employed for a member such as a vane or a rotor which slides at a variable speed or high speed, inertial force or centrifugal force during acceleration or deceleration following sliding and rotation are increased in proportion to the mass. Further, these forces are increased in proportion to the square of an angular speed of rotation. In order to attain a high speed using a ferrous material, therefore, the overall appliance or apparatus must be increased in size and must be extremely strongly manufactured. In addition, there is an apprehension that the efficiency of the apparatus itself is reduced.
Thus, a low specific gravity material has been watched with interest. Magnesium, which is the lightest material, cannot attain matching with peripheral members since its thermal expansion coefficient is too large. Further, it cannot withstand employment as a slide member due to low hardness or low strength.
Then, employment of a lightweight aluminum alloy has been studied. In order to reduce thermal expansion and improve wear resistance in the aluminum alloy, it has been attempted by various manufacturing methods to add mainly Si in a large amount.
First, adding Si by means of an ingot technique such as fusion casting, fusion rolling, continuous casting or the like has been studied, while no satisfactory slide member has been obtained only by dispersion of Si primary crystals. Namely, it has been impossible to provide a slide member which can substitute for a ferrous material unless surface treatment such as hard alumite treatment or Ni-P plating is carried out. Particularly in the case of a vane for a compressor which is subjected to a high speed or a high load and used under a severe sliding condition such as a substitutional florocarbon atmosphere, abrasion damage or seizure takes place. After all, it has been impossible to obtain a wear resistant slide member which can withstand a severe environment even if Si is mainly added in a large amount by means of an ingot technique such as fusion casting, fusion rolling or continuous casting.
Then, an attempt has been made to increase amounts of addition of alloy components of transition metal elements such as Fe, Ni, Cr and the like by improving the solidification rate of the fusion casting method. However, the amounts of metal elements which can form fine intermetallic compounds by being bonded with aluminum are limited. Namely, the limit for the total amount of transition metal elements is about 4 weight %, in order to improve wear resistance without deteriorating strength and toughness in case of dispersing fine intermetallic compounds of an Fe, Ni or Fe--Ni aluminide. If the elements are added in excess of this amount, coarse crystallized substances or deposits are formed at the solidification rate of the fusion casting method, to deteriorate the strength.
When elements of Zr, Ti, Mo and V are added, a matrix is hardened by fine deposits and hence wear resistance can be further improved. When the fusion casting method is employed, however, reduction of the strength is caused if the total sum of the amounts of addition thereof exceeds 1 weight %. It is difficult to add the elements such as Fe, Ni, Mo, Ti, Zr, V and the like in practice due to a problem of segregation in the molten metal and the like, and it has been impossible to implement an aluminum alloy which is so excellent in wear resistance that this aluminum alloy can substitute for a ferrous material with no surface treatment, even if the same are added simultaneously with Si.
In powder metallurgy, on the other hand, it is possible to obtain dispersion-strengthened alloy powder which is fine and has a homogeneous structure by adding the aforementioned transition metal elements in large amounts simultaneously with a large amount of Si by employing a rapid solidification method. If rapidly solidified aluminum alloy powder is employed as a raw material and solidified by powder metallurgy, it becomes possible to prepare a high silicon containing aluminum alloy or a high transition element containing aluminum alloy, which has been impossible to obtain in a fusion method. When fine crystallized substances and deposits thereof are homogeneously dispersed in a matrix, further, wear resistance is improved. It is known that the structure is further refined by increasing the solidification rate for the raw material powder and excellent characteristics are attained in this case.
For example, Japanese Patent Application No. 62-59684 (Japanese Patent Laying-Open No. 1-132734) "Aluminum Alloy for Vane Material", discloses a known material for a vane of an aluminum alloy employing rapidly solidified aluminum alloy powder. However, a satisfactory result has not been attained also in the case of employing such rapidly solidified aluminum alloy powder. In a present rotary compressor for a car air conditioner, switching from the conventional fluorocarbon medium to a substitutional florocarbon medium represented by R134a is in progress. Consequently, the frictional sliding environment between a vane and a cylinder case and between the vane and a rotor in the compressor is more severe due to reduction of the lubrication performance of a solvent. Consequently, abrasion damage and a seizure phenomenon readily take place in the powder aluminum alloy disclosed in Japanese Patent Application No. 62-59684, and further improvement has been awaited as a material for a vane.
As another method of improving wear resistance and seizure resistance of an aluminum alloy, development of a composite material in which hard grains such as ceramic or whisker short fiber are dispersed in an aluminum alloy has been studied.
In Japanese Utility Model Application No. 59-141396 (Japanese Utility Model Laying-Open No. 61-55188) "Vane for Rotary Compressor", for example, the following method has been proposed: SiC, Al.sub.2 O.sub.3 and Si.sub.3 N.sub.4 are selected as hard grains, and 3 to 30 volume % of these hard grains are added and mixed into Al--Si--Fe alloy powder, and a green compact is prepared by cold isostatic pressing (CIP). Thereafter the composite material is solidified by hot extrusion, and this composite material is positioned on a forward end portion of a vane which is under more severe frictional sliding conditions.
Further, Japanese Patent Application No. 59-169016 (Japanese Patent Publication No. 5-33298) "vane" discloses means of mixing 2 to 7 weight % of ceramic of SiC or Si.sub.3 N.sub.4 of 5 to 50 .mu.m in grain size into Al--Si alloy powder, solidifying this mixture and applying the same to a vane. Japanese Patent Application No. 1-290696 (Japanese Patent Laying-Open No. 3-151589) "Composite Vane for Compressor and Method of Manufacturing the Same" discloses means of mixing 1 to 30 volume % of ceramic such as SiC, Al.sub.2 O.sub.3, K.sub.2 Pi.sub.4 O.sub.2 or the like in the form of whiskers or grains to Al--6 to 16 weight % Si alloy powder, solidifying the mixture and applying the same to a forward end portion of a vane.
Further, Japanese Patent Application No. 60-8894 (Japanese Patent Publication No. 6-96188) "Fiber-Reinforced Metal Composite Material" discloses an aluminum alloy prepared by forming a matrix of a hyper-eutectic Al--13 to 30 weight % Si alloy and making this matrix contain 5 to 15 volume % of alumina fiber or aluminasilica fiber of not more than 10 .mu.m in mean diameter.
Further, Japanese Patent Application No. 4-280543 (Japanese Patent Laying-Open No. 5-311302) "Low-Frictional Aluminum Alloy Excellent in High-Temperature Strength and Wear Resistance" discloses an aluminum alloy having a matrix of an Al--10 to 25 weight % Si--5 to 20% Ni--1 to 5% Cu alloy, which is improved in wear resistance and seizure resistance by mixing and molding powder or whisker fiber of a nitride, a boride, an oxide, a carbide or the like into the same.
In every ceramic dispersed aluminum alloy or fiber-reinforced aluminum alloy proposed in the aforementioned manner, however, abrasion damage and seizure of an A390 ingot aluminum alloy of a cylinder case member and an Al--Si--Fe powder alloy of a rotor material readily take place in evaluation of durability wear resistance under unprecedentedly severe substitutional fluorocarbon environment, and further improvement has been demanded. The cause for this is conceivable as follows: The added ceramic is extremely hard and has an effect of remarkably improving heat resistance and hardness by being composed with the aluminum alloy. However, the hard ceramic is weak in adhesion in the interface between the same and the matrix, and hence the ceramic may seperate fall out or away from the matrix during sliding. In this case, the ceramic serves as an abrasive along the sliding surface and hence the vane of the ceramic dispersed aluminum alloy itself is readily worn while seizure to the counter material is readily caused by a new sliding surface. Further, it wears the counter material too.
In the aforementioned method, further, there have been a problem of economy, and a problem of production factors and the like since the high-priced ceramic is employed and the so-called two-layer structurization is carried out on the forward end portion and the plate type portion through different materials.
To this end, development of a vane of an aluminum alloy in substitutional fluorocarbon has been studied. As the result, a method of forming a hard plating layer or a plating layer containing a self-lubricant component on an outer peripheral portion of a vane and a method of forming an ion plating film consisting of a mixed phase of a metal and a nitride are employed at present in view of improving wear resistance and seizure resistance. For example, Japanese Patent Application No. 61-311256 (Japanese Patent Laying-Open No. 63-167092) "Vane Type Compressor" discloses means of forming an ion plating film of titanium nitride on a forward end portion of a vane which is made of an Al--Si alloy and forming an electric plating layer mainly composed of iron on its side surface. Japanese Patent Application No. 63-288508 (Japanese Patent Laying-Open No. 2-136586) "Vane Type Compressor" discloses means of providing a plating layer mainly composed of iron or nickel on a side surface of a vane of an aluminum alloy.
Further, Japanese Patent Application No. 62-186826 (Japanese Patent Laying-Open No. 64-32087) "Vane Type Compressor" discloses means of providing an electrolytic or electroless Ni--P plating layer on an outer surface of a vane which is made of an Al--Si alloy. Japanese Patent Application No. 3-82405 (Japanese Patent Laying-Open No. 4-314868) "Slide Member" discloses means of improving wear resistance and seizure resistance by forming an Ni--P plating or Ni--P/BN or SiC composite plating layer on a surface of a vane of an aluminum alloy.
When surface coating treatment is performed, however, it is necessary to first carry out rough working (primary working) of the surface of the vane material for ensuring dimensional accuracy for providing a surface treated coat. Then, it is necessary to carry out high-priced surface treatment (pretreatment, as the case may be). In a vane requiring further strict dimensional accuracy, finish working (secondary working) by polishing, grinding, etc. is finally required. In the current method of manufacturing a vane of an aluminum alloy requiring a number of steps of primary working.fwdarw.pretreatment.fwdarw.surface treatment.fwdarw.secondary working for finishing a final product from the material of the aluminum alloy, therefore, omission of the surface treatment is the most important subject in view of economy. If the surface treated layer is separated during employment, the vane immediately loses its reliability, as a matter of course.